A conventional clamping assembly of stringing machine is shown in FIG. 1 and generally includes a body 11, a tapered member 12, a base 13, a knob 14 and a slide block 15. The body 11 has a tapered hole 111, a recess 112 and a tube 113 which extends upward from the body 11. The tapered member 12 is engaged with the tapered hole 111 and a protrusion 121 and a stop block 122 are fixed to an underside of the tapered member 12 so as to be connected to the rail of the stringing machine. The tube 113 receives the clamping assembly which is not shown. The base 13 is engaged with the recess 112 and includes a shaft 131 which has an eccentric section 132. A notch 133 is defined in the base 13 and located corresponding to the notch 133. The knob 14 is connected to a top of the shaft 131. A slot 114 is defined between the tapered hole 111 and the recess 112 so that the slide block 15 is engaged with the slot 114. The slide block 15 has a bolt 151 at an end thereof and the bolt 151 faces the recess 112 so as to be in contact with the eccentric section 132 of the shaft 131. A cap 152 is mounted to the contact surface between the bolt 151 and the eccentric section 132. The slide block 15 has an inclined surface 153 which is in contact with tapered member 12 and matches with the tapered member 12.
When positioning the body 11 to prevent the clamping assembly from shifting, the knob 14 is rotated so that the eccentric section 132 pushes the bolt 151 and the slide block 15 moves horizontally such that the tapered member 12 is pushed upward by the inclined surface 153. The stop block 122 is in contact with the rail 19 so that the body 11 is positioned and does not rotate. When the body 11 is to be released from the position, the knob 14 is rotated in opposite direction and the torsion spring 141 in the knob 14 rotates the knob 14 at high speed and back to its original position. The eccentric section 132 of the shaft 131 is not in contact with the bolt 151 so that the stop block 122 is disengaged form the rail 19. The tapered member 12 is lowered due to the gravity and the body 11 is freely rotated and moved along the rail 19.
It is noted that when the knob 14 is rotated to secure the body 11, during the stringing processes, the knob 14 might be rotated unintentionally by the user. Because the clamping assembly does not have a positioning feature, the knob 14 is easily rotated in opposite direction by the torsion spring 141. This shortcoming makes stringing machine to be un-reliable.
Another clamping assembly known to applicant is shown in FIGS. 2 to 4, the clamping assembly comprises a slide member 21, a positioning device 22, a control device 23 and a rail 24. The rail 24 is located at a top of the stringing machine and a slot 242 is defined in the rail 24. The positioning device 22 is located at an end of the slide member 21 and a tube 211 is located at the other end of the slide member 21. An extension 282 of a clamping device 28 is inserted into the tube 211. The control device 23 is located between the positioning device 22 and the tube 211.
The positioning device 22 includes a tapered cap and a stop block 222, wherein the diameter of the cap is reduced gradually from the top to the bottom so that the cap has a tapered outer surface. The cap is slidably engaged with the slot 242 of the rail 24. The stop block 222 is connected to the cap from the underside of the rail 24 by bolts so that the cap moves the stop block 222 which can position the slide member 21.
The control device 23 includes a pin 231, a ring-shaped member 232 and a knob 233. The ring-shaped member 232 is connected to the slide member 21 and the pin 231 is rotatably connected to the ring-shaped member 232. The pin 231 is connected to the knob 233. The ring-shaped member 232 includes a torsion spring 234 which is connected between the slide member 21 and the knob 233 so as to provide a force to return the knob 233.
The tube 211 includes an engaging section 2112 and a receiving section 2114. The receiving section 2114 is inserted into the pivotal hole 216 in the slide member 21 and the stepped lower end of the engaging section 2112 in contact with a top of the slide member 21.
The receiving section 2114 has a positioning pin 217 and a spring 218 which biases the positioning pin 217 such that the positioning pin 217 moves axially. The tube 211 has a slit 2115 which is located in the receiving section 114. The slide member 21 has an insertion slot 219 which communicates with the pivotal hole 216. The insertion slot 219 extends to an underside of the knob 233. The positioning pin 217 includes a piece 2172 and an insertion member 2174. The piece 2172 is received in the receiving section 2114 and the insertion member 2174 is engaged with the insertion slot 219. The piece 2172 and the insertion member 2174 are connected with each other by connection portion 2173 which is pivotably engaged with the slit 2115. The knob 233 is secured by inserting the insertion member 2174 into the pin hole 2334 to prevent the knob 233 from returning unintentionally.
By releasing the clamping device 28 to release the strings, the extension 282 of the clamping device 28 presses the piece 2172 due to the gravity to the clamping device 28 and the positioning pin 217 is then lowered to release the stop status to the knob 233. By rotation of the torsion spring 234, the knob 233 and the pin 231 are returned. The stop block 222 is longer contacts against the rail 24 and the slide member 21 can be rotated and shift to achieve the purpose of adjustment of the clamping device 28. It is noted that the clamping device 28 includes two ridge-groove on two sides thereof so as to firmly clamp the strings. Nevertheless, the clamping device 28 cannot lowered by the gravity because of the ridge-groove surfaces, and the positioning pin 217 cannot release the knob 233. The users then have to adjust the clamping device 28 and the positioning pin 217, this increases the time required to string the sport rackets.
The present invention intends to provide a clamping assembly to improve the shortcoming mentioned above so that the stringing machine is more reliable.